Aluminum alloy sheet for easy-open can ends having excellent corrosion resistance and age softening resistance and its production process

Abstract

An aluminum alloy containing magnesium (Mg) between 3.0 and 4.0 wt. %, manganese (Mn) between 0.5 and 1.0 wt. %, copper (Cu) between 0.2 and 0.6 wt. %, iron (Fe) between 0.05 and 0.4 wt. % and remaining obligatory trace elements, has an electrical conductivity after baking of 30 to 32% IACS, a yield strength of 320 MPa or more and a ratio of decrease in buckling strength after retort-treatment to that immediately after manufacturing the can end of less than 10%. This an aluminum alloy sheet for can ends has an excellent corrosion resistance, complete lack of stress corrosion cracking, or age softening resistance, maintains the a high buckling strength obtained subsequent to the manufacture of a can, even after retort treatment and storage at room temperature. The aluminum alloy sheet of this invention is particularly suitable for use as a can end for non-carbonated beverages and has the potential for even thinner aluminum alloy sheet formation.

We claim: 
     
       1. An aluminum alloy sheet having excellent corrosion and age softening resistance, said aluminum alloy comprising from 3.0-3.6 wt. % Mg, more than 0.5 to not more than 1.0 wt. % Mn, 0.2-0.6 wt. % Cu, 0.05-0.4 wt. % Fe and the balance being aluminum and having an electrical conductivity of 30-32% IACS after heating at 260° C. and a yield strength of at least 320 MPa. 
     
     
       2. A coated aluminum alloy sheet having excellent corrosion and age softening resistance, said sheet being made up of an aluminum alloy comprising from 3.0-3.6 wt. % Mg, more than 0.5 to not more than 1.0 wt. % Mn, 0.2-0.6 wt. % Cu, 0.05-0.4 wt. % Fe and the balance being aluminum and having an electrical conductivity of 30-32% IACS after heating at 260° C., a yield strength of at least 320 MPa and an organic coating provided thereon. 
     
     
       3. A coated aluminum alloy sheet having excellent corrosion and age softening resistance, said aluminum alloy comprising from 3.0-3.6 wt. % Mg, more than 0.5 to not more than 1.0 wt. % Mn, 0.20.6 wt. % Cu, 0.05-0.4 wt. % Fe and the balance being aluminum and having an electrical conductivity of 30-32% IACS after heating at 260° C. and a yield strength of at least 320 MPa. 
     
     
       4. A coated aluminum alloy can end having excellent corrosion and age softening resistance, said can end being of size 204 and having a panel height of 2.3 mm, said can end being made from a sheet of an aluminum alloy coated with an organic resin, said aluminum alloy comprising from 3.0-3.6 wt. % Mg, more than 0.5 to not more than 1.0 wt. % Mn, 0.2-0.6 wt. % Cu, 0.05-0.4 wt. % Fe and the balance being aluminum and having an electrical conductivity of 30-32% IACS after heating at 260° C. and a yield strength of at least 320 MPa, the ratio of decrease in buckling strength of the can end being less than 10% after heating for 30 minutes at 120° C. the buckling strength being determined by seaming the can end with a can body, clamping the seamed portion of the can end and applying an internal pressure until the periphery of the can end begins to deform polygonally.